The discovery of novel and useful materials depends largely on the capacity to make and characterize new compositions of matter. As a result, recent research relating to novel materials having useful biological, chemical, and/or physical properties has focused on the development and implementation of new methods and systems for synthesizing and evaluating potentially useful chemical compounds. In particular, high-speed combinatorial methods have been developed to address the general need in the art for systematic, efficient, and economical material synthesis techniques as well as methods to analyze and to screen novel materials for useful properties.
High-speed combinatorial methods often involve the use of array technologies that require accurate dispensing of fluids each having a precisely known chemical composition, concentration, stoichiometry, ratio of reagents, and/or volume. Such array technologies may be employed to carry out various synthetic processes and evaluations. Array technologies may employ large numbers of different fluids to form a plurality of reservoirs that, when arranged appropriately, create combinatorial libraries. In order to carry out combinatorial techniques, a number of fluid dispensing techniques have been explored, such as pin spotting, pipetting, inkjet printing, and acoustic ejection.
Many of these techniques possess inherent drawbacks that must be addressed, however, before the fluid dispensing accuracy and efficiency required for the combinatorial methods can be achieved. For instance, a number of fluid dispensing systems are constructed using networks of tubing or other fluid-transporting vessels. Tubing, in particular, can entrap air bubbles, and nozzles may become clogged by lodged particulates. As a result, system failure may occur and cause spurious results. Furthermore, cross-contamination between the reservoirs of compound libraries may occur due to inadequate flushing of tubing and pipette tips between fluid transfer events. Cross-contamination can easily lead to inaccurate and misleading results.
Acoustic ejection provides a number of advantages over other fluid dispensing technologies. In contrast to inkjet devices, nozzleless fluid ejection devices are not subject to clogging and their associated disadvantages, e.g., misdirected fluid or improperly sized droplets. Furthermore, acoustic technology does not require the use of tubing or involve invasive mechanical actions, for example, those associated with the introduction of a pipette tip into a reservoir of fluid.
Acoustic ejection has been described in a number of patents. For example, U.S. Pat. No. 4,308,547 to Lovelady et al. describes a liquid drop emitter that utilizes acoustic principles to eject droplets from a body of liquid onto a moving document to result in the formation of characters or barcodes thereon. A nozzleless inkjet printing apparatus is used such that controlled drops of ink are propelled by an acoustical force produced by a curved transducer at or below the surface of the ink. Similarly, U.S. Ser. No. 09/964,212 describes a device for acoustically ejecting a plurality of fluid droplets toward discrete sites on a substrate surface for deposition thereon. The device includes an acoustic radiation generator that may be used to eject fluid droplets from a reservoir, as well as to produce a detection acoustic wave that is transmitted to the fluid surface of the reservoir to become a reflected acoustic wave. Characteristics of the reflected acoustic radiation may then be analyzed in order to assess the acoustic energy level produced by the acoustic radiation generator at the fluid surface. Thus, acoustic ejection may provide an added advantage in that the proper use of acoustic radiation provides feedback relating to the process of acoustic ejection itself.
The ability to predetermine the threshold level of droplet production for a fluid disposed in a reservoir would enable the user to more accurately control droplet size, minimize fluid waste and provide substantially more effective control of the power output of the acoustic energy generating apparatus used in fluid output from the reservoirs. Because the materials having biological, chemical, and/or physical properties useful in combinatorial synthesis can be extremely rare and/or prohibitively expensive, it is desirable to provide effective controls on power output, and consequently drop volume, in their use.
Regardless of the dispensing technique used, however, inventory and materials handling limitations generally dictate the capacity of combinatorial methods to synthesize and analyze increasing numbers of sample materials. For instance, during the formatting and dispensing processes, microplates that contain a plurality of fluids in individual wells may be thawed, and the fluid in selected wells can then be extracted for use in a combinatorial method. When a pipetting system is employed during extraction, a minimum loading volume may be required for the system to function properly. Similarly, other fluid dispensing systems may also require a certain minimum reservoir volume to function properly. Thus, for any fluid dispensing system, it is important to audit or monitor the reservoir contents to ensure that at least a minimum amount of fluid is provided. Such content monitoring generally serves to indicate the overall performance of a fluid dispensing system, as well as to maintain the integrity of the combinatorial methods.
An additional feature desirable in fluid monitoring is the ability to evaluate the properties of the microplate itself. Structural anisotropies at the molecular level, such as variations in the molecular orientation in the polymers used to make the plate, can impact the transmission of acoustic energy through the plate. Variations in molecular orientation lead to variations in the reflected acoustic energy from both the plate interface with the reservoir fluid as well as the reservoir fluid interface with the atmosphere. Such variations need to be accounted for or they will be attributed erroneously to variations in composition measurements, fluid height detection and the amount of energy reaching the surface.
In addition, during combinatorial synthesis or analysis processes, environmental effects may play a role in altering the reservoir contents. For example, dimethylsulfoxide (DMSO) is a common organic solvent employed to dissolve or suspend compounds commonly found in drug libraries. DMSO is highly hygroscopic and tends to absorb any ambient water with which it comes into contact. In turn, the absorption of water dilutes the concentration the compounds as well as alters the ability of the DMSO to suspend the compounds. Furthermore, the absorption of water may impact the transmission properties of acoustic energy transmitted through a DMSO/water mixture and other water-sensitive compounds.
U.S. Pat. No. 5,880,364 to Dam, on the other hand, describes a non-contact ultrasonic system for measuring the volume of liquid in a plurality of containers. An ultrasonic sensor is disposed opposite the top of the containers. A narrow beam of ultrasonic radiation is transmitted from the sensor to the open top of an opposing container to be reflected from the air-liquid interface of the container back to the sensor. By using the round trip transit time of the radiation and the dimensions of the containers being measured, the volume of liquid in the container can be calculated. This device cannot be used to analyze wave forms of acoustic energy in fluid in sealed containers. In addition, the device lacks precision because air is a poor conductor of acoustic energy. Thus, while this device may provide rough estimate of the volume of liquid in relatively large containers, it is unsuitable for use in providing a detailed analysis of the wave forms of acoustic energy in fluids in reservoirs typically used in combinatorial techniques. In particular, this device cannot determine the position of the bottom of containers since substantially all of the emitted acoustic energy is reflected from the liquid surface and does not penetrate to detect the bottom. Small volume reservoirs such as microplates are regular arrays of fluid containers, and the location of the bottoms of the containers can vary by a significant fraction of the nominal height of a container due to distortions in the plate, such as bowing. Thus, detection of only the position of the liquid surface leads to significant errors in height and thus volume estimation in common containers.
Thus, there is a need in the art for improved methods and apparatuses that are capable of efficiently delivering fluid to a plurality of reservoirs, a capability that is particularly useful in synthetic and analytical processes to increase the robustness, efficiency, and effectiveness of the combinatorial techniques employed therein.
There is a need in the art to determine the energy level of an acoustic pulse to a site at the surface of a fluid in a reservoir and the ability to process the reflected energy of that pulse to be able to raise the amplitude of succeeding pulses to an energy level sufficient to form a droplet, i.e., threshold level. There is a need to analyze the input energy level of a pulse having an energy level sufficient to disturb or perturb the surface of the fluid in the reservoir but lower than threshold level, i.e., a sub-threshold pulse, in order to be able to generate a subsequent pulse having a sufficient acoustic energy level to form a droplet. There is a need in the art for a method to map non-uniformities in the wells contained in a well plate. There is a need in the art to be able to effectively calibrate the power system used to generate acoustic energy.